1. Field of the Invention
The present invention relates to a roller and a process for producing the same. More particularly, it pertains to a roller such as a developer conveying roller (also referred to as "developer feed roller"), electrifying roller, transfer roller, developing roller, cleaning roller and paper feed roller each to be used in an electrophotographic apparatus or electrostatic recording apparatus such as a copying machine and printer; and to a process for producing said roller.
2. Description of Related Arts
An electrophotography recording apparatus which is widely utilized for a copying machine, a laser beam printer and the like is equipped generally with a photosensitive body in the form of a drum (herenafter referred to as "photosensitive drum") and functions so as to form an electrostatic latent image by carrying out electrification and exposure against said photosensitive drum; then allow a developer such as a toner (hereinafter sometimes referred to as "toner") to adhere to the photosensitive drum in accordance with the latent image on the drum to proceed with development; subsequently transfer the toner on the drum to a recording medium such as a recording sheet for the purpose of image transfer; thereafter electrically discharge the drum to a prescribed potential and clean the toner remaining on the drum; and then prepare the recording. The toner carried on the recording medium by means of image transfer is fixed onto the recording medium by being molten and pressure stuck, thus completing a series of recording work.
In the following, simple description will be given of the conveyance of the developer in the aforesaid series of recording work. Specifically, for example, a developer which is filled in a developing apparatus is fed to the surfaces of a developing roller by means of a developer conveying roller (developer feed roller) and is regulated to a uniform thin layer by a blade. While the developing roller is rotated in contact with or in close proximity to a photosensitive drum under the above-mentioned developer condition, the developer is stuck to the electrostatic latent image on the drum from the developing roller to visualize said latent image.
With recent progress of electrophotographical technique, a variety of requisite characteristics come to be imposed upon a roller such as a developer conveying roller, electrifying roller, transfer roller, developing roller, cleaning roller and paper feed roller each being used in an electrophotography recording apparatus. One of the aforesaid requisite characteristics is that an alteration be made in the surface conditions of only an arbitrary part of a roller.
The reason for such requisite characteristics being demanded varies depending upon the type of a roller as described hereunder. In the case of an electrifying roller, transfer roller, developing roller and cleaning roller, there have been a problem in which since the roller is rotated in contact with a photosensitive drum, the frictional force between the roller and the drum, when being excessively strong, results in a large-sized electric motor for driving the roller, the need for replacing the existing electric power source with a power source having a larger capacity.
On the other hand, in the case of a paper feed roller, whose general structural drawing is given in FIG. 3, a shaft 21 is equipped with ring bodies 22 made of a synthetic resin, over which are fitted rubbery elastic layers 23. Such a paper feed roller in which a shaft 21 is equipped in advance, with a plurality of elastic layers 23 is directed to the prevention of meandering of a recording medium which feeds sheets of paper. However, a paper feed roller of such a structure has involved the problems of intricate and large number of production steps and consequent high production cost.
In addition, the developer conveying roller is called upon (1) to make an elastic layer low in hardness, smoothen its surface, secure a nip between the developer conveying roller and the developing roller and ensure a sufficient amount of a developer to be conveyed; (2) to enhance the density of cells on and around the surface of the developer conveying roller so as to prevent the surface thereof from being clogged with the developer; and (3) to eliminate scuffing on the surface of the developer conveying roller and prevent foreign matters such as a foam and cellular material from mixing in a developing apparatus.
Under such circumstances, various methods have been developed for the purpose of producing a developer conveying roller which satisfies the requisite characteristics in the preceding items (1) through (3). The above-developed methods, however, have both advantages and disadvantages, thus failing to readily produce a developer conveying roller which simultaneously satisfies all the aforestated requisite characteristics.